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Chapter 8

Chapter 8. Decision Making Using the IF and EVALUATE Statements. COBOL Statements. Two categories Conditional statements Performs operations depending on existence of some condition Coded with IF-THEN-ELSE structure Imperative statements Performs operation regardless of existing conditions

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Chapter 8

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  1. Chapter 8 Decision Making Using the IF and EVALUATE Statements

  2. COBOL Statements Two categories • Conditional statements • Performs operations depending on existence of some condition • Coded with IF-THEN-ELSE structure • Imperative statements • Performs operation regardless of existing conditions • MOVE, ADD are examples in COBOL

  3. IF Statement IF condition-1 [THEN] imperative statement-1 … [ELSE imperative statement-2 …] [END-IF] Format

  4. ELSE is Optional ELSE is Optional • May be omitted if operation required only when condition exists If Acct-Balance < 0 Then Display 'Account overdrawn' End-If • DISPLAY executed if Acct-Balance less than zero, otherwise it is ignored

  5. Four Types of IF Statements • Relation Condition • IF WS-LINE-COUNT EQUAL 53 • Class Condition • IF WS-PAY-RATE IS NUMERIC • Sign Condition • IF QTY-ON-HAND IS POSITIVE • Condition-name • IF END-OF-INPUT-FILE

  6. Relational Operators Symbols for simple relational conditions SymbolMeaning < is less than > is greater than = is equal to <= less than or equal to >= greater than or equal to

  7. Nested Conditional • IF statement itself can contain additional IF statements • Pair each IF with an END-IF • Used when more than two conditions need to be tested

  8. Compound Conditional • To test for several conditions with one statement • Code multiple conditions separated by ORs or ANDs

  9. OR Compound Conditional • Use OR to test whether any one of several conditions exists IF A = B OR B > 12 Add A TO Total ELSE ADD 1 TO Count END-IF Executed if either condition exists Executed only if A not = B and B <= 12

  10. AND Compound Conditional • Use AND to test if all of several conditions are met IF A = 5 AND B > 0 ADD 10 TO A ELSE MOVE 0 TO B END-IF Executed if both simple conditions met Executed if one or both simple conditions not met

  11. AND and OR in Conditionals • Compound conditions may include both AND and OR • Hierarchy rules • Conditions with AND evaluated first from left to right • Conditions with OR evaluated last from left to right • Parentheses used to override this order

  12. AND and OR in Conditionals If Q > 0 Or R < S And R = 10 Multiply 2 By Q End-If Test conditions in this order: 1. R < S And R = 10 OR 2. Q > 0 Example

  13. Negating Conditionals • NOT placed before conditional reverses its truth value ConditionResult If Amt Not = 10 True if Amt is 15 False if Amt is 10 If Amt Not > 8 True if Amt is 2 False if Amt is 12

  14. Negating Compound Conditionals • To negate compound conditional place it in parentheses, precede it with NOT • Condition to check for In-Code of S or D If In-Code = 'S' Or In-Code = 'D' • To negate this condition (check for In-Code that is neither S nor D) If Not (In-Code = 'S' Or In-Code = 'D')

  15. Sign Tests • To test whether field is POSITIVE, NEGATIVE or ZERO ConditionResult If Amt Is Positive True if Amt is greater than 0 If Amt Is Negative True if Amt is less than 0 If Amt Is Zero True if Amt equals 0

  16. Class Test • To test whether type of data if field is numeric or alphabetic ConditionResult If Amt Is Numeric True if Amt = 153 False if Amt = 15B If Code Is Alphabetic True if Code = PQR False if Code = P23

  17. Defining Condition-Names 05 Pay-Code Pic X. 88 Hourly Value 'H'. 88 Salaried Value 'S'. • Define field in DATA DIVISION • Use level 88 to define condition-name and associated value Example

  18. Using Condition-Names • Use any place a condition can be used in PROCEDURE DIVISION If Hourly Perform Calc-Hourly-Pay End-If • If Pay-Code field has a value of 'H', condition Hourly is true • Hourly same as condition Pay-Code='H'

  19. EVALUATE Statement • Used to implement Case structure • Tests for series of conditions • May be used in place of IF statement • Often code clearer, more efficient with EVALUATE when multiple condition need to be checked

  20. EVALUATE Statement identifier-1 EVALUATE expression-1 WHEN condition-1 imperative-statement-1 … [WHENOTHER imperative-statement-2 …] [END-EVALUATE] Format

  21. The EVALUATE Statement EVALUATE STU-CLASS WHEN “FR” PERFORM 110-FRESHMANWHEN “SO” PERFORM 120-SOPHOMOREWHEN “JR” PERFORM 130-JUNIORWHEN “SR” PERFORM 140-SENIOR WHEN “GS” PERFORM 150-GRADUATE WHEN OTHER PERFORM 199-ERROR END-EVALUATE

  22. Decision Table • Often used to list conditions and actions to be performed

  23. Code for Decision Table If Code = 'T' If N > 10 Multiply .15 By N Else Multiply .25 By N End-If Else Move 0 To N End-If Delimits inner IF Delimits outer IF

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